A fuel cell system can be used as an auxiliary power supply, i.e., as a so-called “APU,” where APU stands for “Auxiliary Power Unit” in a motor vehicle which is equipped with an internal combustion engine. During a normal drive mode of the vehicle, i.e., with internal combustion engine switched on, the internal combustion engine usually drives a generator, a so-called “electric generator,” via which all electrical components of the vehicle are supplied with power. During operating breaks, i.e., with the vehicle being stationary, it may be necessary to additionally supply certain electrical components of the vehicle with power. This can only be guaranteed to a limited extent by means of a battery of the vehicle. However, as soon as larger power consumers, e.g., an air conditioning unit, shall also remain switched on in such an operating break, a vehicle battery is not sufficient. Hence, it is further prevalent that during such an operating break, the internal combustion engine continues to remain switched on and, e.g., is operated in an idle operating state. In this idle operating state, the internal combustion engine continues to work, however, outside its optimal efficiency, such that this power production is comparatively expensive.
To be able to save fuel during such operating breaks, fuel cell systems such as APUs are used. Such a fuel cell system usually comprises at least one fuel cell in which an electrolyte separates a cathode side from an anode side. Usually, here, a plurality of single fuel cell elements are stacked one on top of another to form a fuel cell stack. A hydrogen-containing anode gas is fed to the anode side, while an oxygen-containing cathode gas is fed to the cathode side. The cathode gas is usually air. The anode gas can be generated by means of a reformer, in particular by means of catalytic conversion, from a hydrogen-containing fuel, and the product of the reformer is usually designated as reformate gas. The reformer advantageously uses the same fuel as the internal combustion engine. A fuel cell, which can process hot reformate gas, which is produced by a reformer, is usually a solid fuel cell or high-temperature fuel cell, which is, as a rule, also designated as “SOFC,” where SOFC stands for “Solid Oxide Fluid Cell.” Such a fuel cell system, especially in the form of an SOFC is, as a rule, optimized for at least one predetermined nominal operating state, in which each of the individual components of the fuel cell system has a predetermined operating temperature. In order to protect the individual components against an excessive thermal and mechanical stress when starting such a fuel cell system, and to keep the energy consumption as low as possible when starting the fuel cell system, it is necessary to carry out a predetermined start procedure or a predetermined start routine, which takes up comparatively much time. The starting of the APU at the beginning of an operating break is therefore accompanied by a certain loss of comfort.
A process for operating a fuel cell system, in which a control device of the fuel cell system is coupled with a navigation device of the vehicle, in such a way that the control device recognizes a foreseeable arrival time from the navigation device, is known from DE 10 2008 063 088 A1. The prior-art operating process assumes that the fuel cell system is switched on during the drive mode of the vehicle and should be switched off when reaching the travel goal. In the prior-art process, the control device calculates a time for activating a switch-off procedure or switch-off routine for the fuel cell system to be able to switch this off as gently as possible for the individual components.
Such a switch-off procedure also requires comparatively much time. The control device can now select the time for activating the switch-off procedure in a specific manner, such that the switch-off procedure is essentially completely finished at the travel end time determined by the navigation device, such that the end of the switch-off procedure essentially coincides with the travel end.